The subject of the invention concerns a method of drawing ribs on bimetallic tubes, in which the ribs are drawn from an external tube into which initial compressive stress has been introduced.
Ribs on tubes are drawn by acting on the tube with rotary tools comprising roll-formed disks. From the Polish patent specification, application No. P-241323, a method of drawing ribs on tubes is known, in which before placing the tube in the zone of the action of disk tools initial compressive stress is introduced into the tube. In this way a discharge has been achieved during the operation of the tool from axial loads bending out the roll-formed disks practically from the first stage of the working contact of the tool with the tube. For the purpose of inducing compressive stresses in the tube in the application No. P-241323 a is provided.
In the case of drawing ribs on bimetallic tubes such a solution is practically useless because it is difficult to meet the requirement of accurately setting both tubes in relation to each other with simultaneous application of a compressive force on the external tube.